Modern electronic systems require that signals be transmitted with ever-increasing speed and low error rates. This necessitates a transmisson line and associated interconnections between a signal source, such as a transmitter or line driver, and a load, such as a receiver, which match the characteristic impedance of the signal source and load while exhibiting low loss or attenuation.
To effect these results it has been found necessary to utilize transmission line techniques designed for the particular application. Printed circuit boards had previously been manufactured with no particular attention to the impedance characteristics, i.e., dynamic resistance, of the signal carrying conductors. Such circuit boards are generally now being constructed with all the structural and functional characteristics of transmission lines, with signal carrying conductors placed at a known preestablished distance from a reference plane and separated from the reference plane by insulation of known, preestablished electrical characteristics. While printed circuit boards themselves are being designed and fabricated today with attention to the desired transmission line characteristics, unless the entire electrical package or system is provided with the desired transmission line characteristics, including connectors between the circuit boards, the overall system is degraded and unable to achieve an operating performance with the desired accuracy and speed.
Types of transmission lines for use in transmitting electrical signals, whether in circuit boards or in connectors, include microstrip, stripline and coax. Microstrip geometry is characterized by a reference or ground plane on one side only of, and parallel with, the signal carrying conductors. Stripline geometry is similar to microstrip but employs two parallel reference or ground planes with the signal carrying conductors parallel to one another and between the ground planes. The third transmission geometry, coax, is characterized by the signal carrying conductors being individually surrounded by the reference or ground plane.
One arrangement for providing coaxial cable transmission line connections between printed circuit boards is disclosed in U.S. Pat. No. 3,689,865 to Pierini. While satisfactory from a technical standpoint, this arrangement is less than desirable when constructing high density electrical connectors because such an arrangement for circuit board connection is bulky and reduces the density of the interconnections to an undesirably low level.
Other types of printed circuit board connectors designed to maintain the circuit transmission line impedance characteristics are disclosed in U.S. Pat. Nos. 4,418,972 to Benasutti; 3,651,432 to Henschen; 3,643,201 to Harwood; 4,133,592 to Cobaugh; and 3,871,728 to Goodman as well as Technical Bulletin Number 237 to Teradyne. While these connectors constitute improvements over the connectors employing discrete coaxial cables, such connectors are of limited utility due to less than optimum operational characteristics such as pin utilization inefficiencies.
By way of example, the apparatus disclosed in the Benasutti patent reduces impedance but does not control it. The Teradyne apparatus may inherently provide some impedance control for the exterior pin adjacent the ground plane but not for the remainder of the pins. The Henschen and Harwood patents require using every other signal pin to control impedance. The Goodman patent attempts to simulate coax. The Cobough patent gives no impedance control whatsoever. The prior art simply fails to teach connector geometry to allow microstrip transmission of electrical signals through connectors.
The present invention also constitutes an improvement over the printed circuit board connectors disclosed in commonly assigned U.S. Pat. No. 4,616,893 in the name of Feldman and U.S. patent application Ser. No. 733,176 filed May 13, 1985 in the name of Feldman et al.
As illustrated by the large number of prior patents and other disclosures, efforts are continuously being made in an attempt to efficiently, quickly, accurately and economically transmit electrical signals. None of these disclosures, however, suggests the present inventive combination of connector elements for transmitting electrical signals through the controlled characteristic impedance of microstrip transmission techniques as herein described and claimed. This invention achieves its purposes, objects and advantages over the prior art through new, useful and unobvious components which increase user convenience, consistently insure high data transmission rates with low error rates and effect a reduction in cost through the use of a minimum number of functioning parts. All this is attained through the utilization of only readily available materials and conventional components.
These purposes, objects and advantages should be construed as merely illustrative of some of the more prominent features and applications of the present invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention within the scope of the disclosure. Accordingly, other objects and advantages as well as a fuller understanding of the invention may be had by referring to the summary of the invention and detailed description describing the preferred and alternate embodiments of the invention in addition to the scope of the invention as defined by the claims taken in conjunction with the accompanying drawings.